» Jupiter has rocky and icy core more than twice as large as previously thought

Jupiter has rocky and icy core more than twice as large as previously thought

Published: Wednesday, November 26, 2008, 11:09 [IST]

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Washington, Nov 26 : Computer simulations have indicated that Jupiter has a rocky core, surrounded by layer of ice, that is more than twice as large as previously thought.

The simulations have been developed by a geophysicist at the University of California, Berkeley, who simulated conditions inside Jupiter on the scale of individual hydrogen and helium atoms.

The simulation predicts the properties of hydrogen-helium mixtures at the extreme pressures and temperatures that occur in Jupiter's interior, which cannot yet be studied with laboratory experiments.

Applying techniques originally developed to study semiconductors, UC Berkeley's Burkhard Militzer, an assistant professor of earth and planetary science and astronomy, calculated the properties of hydrogen and helium for temperature, density and pressure at the surface all the way to the planet's center.

Coauthor William B. Hubbard, professor of planetary sciences at the University of Arizona's Lunar and Planetary Laboratory in Tucson, used the theoretical data to build a new model for Jupiter's interior.

A comparison of this model with the planet's known mass, radius, surface temperature, gravity and equatorial bulge implies that Jupiter's core is an Earth-like rock 14 to 18 times the mass of Earth, or about one-twentieth of Jupiter's total mass, according to Militzer.

Previous models predicted a much smaller core of only 7 Earth masses, or no core at all.

The simulation suggests that the core is made of layers of metals, rocks and ices of methane, ammonia and water, while above it is an atmosphere of mostly hydrogen and helium.

At the center of the rocky core is probably a metallic ball of iron and nickel, just like Earth's core.

"Our simulations show there is a big rocky object in the center surrounded by an ice layer and hardly any ice elsewhere in the planet," Militzer said.

"This is a very different result for the interior structure of Jupiter than other recent models, which predict a relatively small or hardly any core and a mixture of ices throughout the atmosphere," he added.

"This new calculation by Burkhard removes a lot of the old uncertainties of the 19-year-old model we have had until now," Hubbard said. "The new thermodynamic model is a more precise physical description of what's going on inside Jupiter," he added.

"According to the core accretion model, as the original planetary nebula cooled, planetesimals collided and stuck together in a runaway effect that formed planet cores," Militzer said.

"If true, this implies that the planets have large cores, which is what the simulation predicts," he added.